The iPhone 5 has been a sales success for most carriers around the world. However, Cricket Wireless – the no contract prepaid network operated by Leap Wireless -- isn't having luck selling the iPhone 5 and is seeing stock levels climb as consumers opt for other devices.

Leap Wireless says that it believes it will sell about half as many iPhones as it committed to sell during the first year of its contract with Apple, which ends in June. Leap Wireless believes that the poor sales could leave it with as much as $100 million worth of unsold iPhones by the middle of 2013.

Leap Wireless has 5.3 million subscribers and areas where it can sell the iPhone are limited by its limited network coverage. Leap was the first of the major prepaid carriers in the US to offer the iPhone last year.

Perhaps the biggest challenge facing Leap Wireless and other prepaid carriers who offer the iPhone is one of cost. While carriers that require a contract, such as AT&T and Verizon, are able to subsidize the cost of the iPhone making it significantly cheaper up front, Leap charges the full retail price of $500.

Considering that pre-paid carriers tend to attract customers shopping on a budget coming up with $500 could be a stretch for many subscribers leading them to “cheaper”, subsidized phones.